1. Field of the Invention
This invention relates generally to storage networks and, more specifically, to a network device on a storage network that uses referrals to successively authorize a client on multiple file servers.
2. Description of the Related Art
In a computer network, NAS (Network Attached Storage) file servers connected directly to the network provide an inexpensive and easily configurable solution for a storage network. These NAS file servers are self-sufficient because they contain file systems that allow interoperability with clients running any operating system and communication using open protocols. For example, a Unix-based client can use the NFS (Network File System) protocol by Sun Microsystems, Inc. of Santa Clara, Calif. and a Windows-based client can use CIFS (Common Internet File System) by Microsoft Corp. of Redmond, Wash. to access the same files on a NAS file server. Thus, NAS file servers provide true universal file access.
By contrast, more expensive and powerful SAN (Storage Area Network) file servers use resources connected by Fibre Channel on a back-end, or a dedicated network. A SAN file system is part of the operating system or an application running on the client. But heterogeneous client operating systems may require additional copies of each file to be stored on the storage network to ensure compatibility on the SAN file server. Additionally, communication between clients and file servers on a SAN use proprietary protocols and thus are typically provided by a common vendor. As a result, NAS file servers are preferred when price and ease of use are major considerations. However, the benefits of NAS storage networks over SAN storage networks also have drawbacks.
One drawback with NAS file servers is that there is no centralized control. Accordingly, each client must maintain communication channels between each of the NFS file servers separately. When NAS file servers are either added or removed from the storage network, each client must mount or unmount directories for the associated storage resources as appropriate. This is particularly inefficient when there are changes in hardware, but not in the particular files available on the network, such as when a failing NAS file server is swapped out for an identically configured back-up NAS file server.
However, when a proxy server is introduced between clients and NAS file servers, a number of issues arise. The proxy must form connections with multiple file servers, which requires authentication with each of them on behalf of the user on the client. This is problematic because the proxy must have a password, or hashing thereof, to respond to server challenges. The proxy could connect to one of the NAS file servers, and pass through an authentication challenge from the file server, and pass back a response from the client, but this technique only allows the client to connect to that one file server. In order to connect with additional file servers, the proxy would be required to responds to the file server challenges itself. A proxy serving numerous users would thus be required to store all of those passwords, thereby introducing an additional security risk. Furthermore, the proxy server would have to maintain password updates.
Additionally, the proxy server introduces protocol dialect issues. For each connection with a file server, the proxy server negotiates a single protocol dialect. The proxy server separately negotiates a single protocol dialect with each client, which can be different from that of the file server connection. As a result, these clients would not be able to communicate with the file server.
Therefore, what is needed is a robust network device to authorize a client with several file servers to provide secure transparency of decentralized file servers such as NAS file servers. Furthermore, the network device should enable communications between a client and a file server using different protocol dialects.